BitVM Optimization Exploration

1. Introduction

Bitcoin, as a decentralized digital asset, holds significant importance, but its scalability has always been a challenge. The UTXO model of Bitcoin leads to a stateless system, making it difficult to perform complex computations. To address this issue, technologies such as state channels, sidechains, and client-side validation have emerged, but they all have certain limitations.

In December 2023, the ZeroSync project proposed the BitVM solution, aiming to achieve Turing-complete Bitcoin contracts without changing the Bitcoin consensus. BitVM utilizes Bitcoin scripting and Taproot technology to implement optimistic Rollups, greatly expanding the application scenarios of Bitcoin.

However, BitVM is still in the early stages and has some issues regarding efficiency and security. This article will propose some optimization ideas to further improve the performance of BitVM.

2. BitVM Principle

BitVM is an off-chain contract solution that implements stateful Bitcoin scripts through Lamport one-time signatures. It uses a challenge-response mechanism to perform computations off-chain and verification on-chain.

The core components of BitVM include:

• Circuit commitment: Compiling the program into a binary circuit and committing it in the Taproot address.
• Challenge and Response: Pre-sign a series of transactions to implement the challenge-response game
• Penalty mechanism: Punishments for incorrect declarations

3. BitVM Optimization

3.1 Reducing OP interaction times based on ZK

Zero-knowledge proofs can be introduced to reduce the number of challenges in BitVM and improve efficiency. By verifying ZK proofs instead of the original algorithm, the challenge cycle can be significantly shortened. In the future, the On-Demand ZK Proof model can be explored, generating ZK proofs only when challenges occur.

3.2 Bitcoin-friendly one-time signature

The Winternitz one-time signature scheme can be used as a substitute for the Lamport signature to reduce the length of the signature and public key. By using the Winternitz signature with appropriate parameters in BitVM, transaction fees can be reduced by at least 50%.

3.3 Bitcoin-friendly hash function

A Bitcoin-friendly hash implementation can be designed based on the BLAKE3 hash function to support Merkle inclusion proof verification. The characteristics of BLAKE3 make it suitable for implementation in Bitcoin scripts, significantly reducing the on-chain data required.

3.4 Scriptless Scripts BitVM

By leveraging Scriptless Scripts technology, BitVM's logic gate commitments can be realized using Schnorr multi-signatures and adapter signatures, thereby saving script space and improving efficiency.

3.5 Permissionless Multi-Party Challenge

Research can be conducted on permissionless multiparty OP challenge protocols, extending the trust model of BitVM to a broader scope. Issues such as Sybil attacks and delay attacks need to be addressed, along with the design of appropriate staking and penalty mechanisms.

4. Conclusion

The BitVM technology is still in its early stages, and there is significant room for optimization in the future. Through the exploration and practice of the aforementioned optimization directions, it is expected to further enhance the performance of BitVM, contributing to the scalability and ecological prosperity of Bitcoin.